Source Of Oxygen Atoms Research Articles

Insight into the mechanism of H2O promoted CaCO3 decomposition in CO2 atmosphere

Calcium looping is one of the most promising CO2 capture technology. The flus gas during the calcination stage of the calcium looping contains both CO2 and H2O. However, the effect of H2O on the decomposition of carbonation in the CO2 atmosphere remains inconclusive. This study employed the Reactive Force Field molecular dynamics (ReaxFF-MD) simulations to investigate the influence of H2O on the decomposition of calcium carbonate in a CO2 atmosphere. The TGA experiments demonstrated that H2O increases the decomposition rate of calcium carbonate and also reduces the reaction temperature. Subsequently, the effects of varying CO2 and H2O concentrations on the decomposition of calcium carbonate were examined using ReaxFF-MD simulations. The simulation results for calcium carbonate decomposition, with the addition of CO2 and H2O, aligned with the experimental trends, verifying the reliability of the models. By tracking and labeling carbon, oxygen and hydrogen atom sources in the simulation, the decomposition, carbonation and hydrolysis reaction network for the CaCO3 decomposition in CO2 atmosphere was systematically constructed. Analysis of the chemical reactions and atomic distribution indicated that H2O primarily facilitates calcium carbonate decomposition by generating HCO3− through surface hydrolysis, which reduces the activation energy of the reaction. Moreover, the hydroxyl groups formed by hydrolysis compete with atmospheric CO2 for active sites on CaO, further inhibiting the carbonation reaction and increasing the calcination rate.

Effect of semifluoroalkyl substituents in the POSS on atomic oxygen exposure

Due to the many recent Earth observation missions, very low Earth orbit (VLEO) have become a pressing topic for satellite research. Since the density of atomic oxygen (AO) in VLEO is higher than in low Earth orbit (LEO), the need for AO-resistant materials based on polyhedral oligomeric silsesquioxane (POSS) is strong. However, the effects of the side-chain groups in the POSS on AO exposure are unclear. In this study, we focused on POSS molecules modified with semifluoroalkyl groups as side chains because fluorocarbon groups, such as fluorinated ethylene propylene (FEP), are known to have high AO resistance. Semifluoroalkyl- and alkyl-substituted POSS films were fabricated and exposed to a laser-detonation AO source. Microbalance measurements showed that the mass losses of the semifluoroalkyl-substituted POSS films were larger than those of alkyl-substituted POSS films. X-ray photoelectron spectroscopy measurements showed that the silica layers formed on the semifluoroalkyl-substituted POSS were thicker than on alkyl-substituted POSS films. Surface observation using a field emission scanning electron microscope revealed microscale cracks on the surface of the semifluoroalkyl-substituted POSS. These findings indicate that POSS molecules with fluorine substituents warrant careful consideration of the AO-barrier performance of the silica layer formed during AO exposure.

Manganese-Mediated Electrochemical Oxidation of Thioethers to Sulfoxides Using Water as the Source of Oxygen Atoms.

Oxygen-atom transfer reactions are a prominent class of synthetic redox reactions that often use high-energy oxygen-atom donor reagents. Electrochemical methods can bypass these reagents by using water as the source of oxygen atoms through pathways involving direct or indirect (mediated) electrolysis. Here, manganese porphyrins and related mediators are shown to be effective molecular electrocatalysts for selective oxidation of thioethers to sulfoxides, without overoxidation to the sulfone. The reactions proceed by proton-coupled oxidation of a MnIII-OH2 species to generate a MnIV-OH and MnV═O species. This methodology is compared to direct electrolysis methods initiated by single-electron oxidation of the thioether, and chloride-mediated electrochemical oxidation of thioethers. The Mn-mediated reactions operate at lower applied potential and exhibit improved substrate scope and functional group compatibility relative to direct electrolysis, and the tunability of the Mn-based mediators allows for improved performance relative to chloride-mediated electrolysis. An electrochemical parallel screening platform is developed and applied to a library of pharmaceutically relevant thioethers.

Highly Selective Electrochemical Baeyer-Villiger Oxidation through Oxygen Atom Transfer from Water.

The Baeyer-Villiger oxidation of ketones is a crucial oxygen atom transfer (OAT) process used for ester production. Traditionally, Baeyer-Villiger oxidation is accomplished by thermally oxidizing the OAT from stoichiometric peroxides, which are often difficult to handle. Electrochemical methods hold promise for breaking the limitation of using water as the oxygen atom source. Nevertheless, existing demonstrations of electrochemical Baeyer-Villiger oxidation face the challenges of low selectivity. We report in this study a strategy to overcome this challenge. By employing a well-known water oxidation catalyst, Fe2O3, we achieved nearly perfect selectivity for the electrochemical Baeyer-Villiger oxidation of cyclohexanone. Mechanistic studies suggest that it is essential to produce surface hydroperoxo intermediates (M-OOH, where M represents a metal center) that promote the nucleophilic attack on ketone substrates. By confining the reactions to the catalyst surfaces, competing reactions (e.g., dehydrogenation, carboxylic acid cation rearrangements, and hydroxylation) are greatly limited, thereby offering high selectivity. The surface-initiated nature of the reaction is confirmed by kinetic studies and spectroelectrochemical characterizations. This discovery adds nucleophilic oxidation to the toolbox of electrochemical organic synthesis.

Electrocatalytic Epoxidation of Cyclooctene on Surface Modified Ni Foam Using Water as Oxygen Source.

Electrochemical epoxidation of olefins using water as an oxygen atom source is emerging as an alternative approach for an atom economic and sustainable method towards a highly selective synthesis of epoxides. We report an electrochemical procedure for epoxidation of cyclooctene using water as the sole oxygen atom source over a sodium dodecyl sulfonate (SDS) modified nickel hydroxide Ni(OH)2 catalyst directly grown on Ni foam. The SDS modification facilitates the mass transfer of cyclooctene towards the anode, thus achieving a 2.5-fold higher conversion with more than 90 % selectivity towards the corresponding epoxide compared with pure Ni(OH)2 catalyst.

Alkyne Oxidation by a Vitamin B2-Based Photocatalytic System with Both H2O and O2 as the Oxygen Source.

The employment of readily available photocatalysts and green oxygen atom sources is recognized as a promising strategy to develop sustainable catalysis for oxidation reactions. We herein reported a sacrificial reagent-free system consisting of riboflavin tetraacetate (RFT), an ester of natural vitamin B2 as the photocatalyst, and Sc(OTf)3 and NaCl as the cocatalysts for alkyne oxidation under blue light or even sunlight irradiation to produce 1,2-diketone in which the oxygen atoms were from both water and molecular oxygen, respectively. A major Cl-/Cl• cycle was proposed to be involved and achieved by the excited [RFT-2Sc3+]* complex via single electron transfer for the first time, distinguished from the OCl- active species by a two-electron process in previous flavin-halide photo-oxidation systems.

Relevance of C/O ratios in the gas-phase synthesis of freestanding few-layer graphene

In microwave-plasma synthesis of few-layer graphene from hydrocarbon precursors, the carbon-to-oxygen and the carbon-to-hydrogen ratios are known to influence the product ratio of graphene to amorphous soot-like particles. While the role of oxygenated hydrocarbons and water as oxygen-supplying species has been studied before, in this paper, we compare the effect of carbon dioxide, molecular oxygen, and nitrous oxide mixed with ethylene to systematically change the C/O ratio while keeping the hydrogen supply constant. Ex situ powder analysis, emission spectroscopy, gas chromatography, and simple reaction kinetics simulations are employed to evaluate and describe the synthesis process. Additionally, thermophoretically sampled nanomaterials are collected close after the first particle inception and analyzed ex situ. The results show that molecular oxygen and nitrous oxide increase the graphene fraction with decreasing C/O ratios and pure graphene is reached at 2:1.5. The decrease in C/O ratio results in an overall decrease in solid carbon yield. With carbon dioxide, pure graphene cannot be generated at a C/O ration of 2:1.5, although a similar reduction of the particle yield is observed. Thermophoretic sampling showed that the specific mixture of carbon allotropes is already defined a few cm downstream to the plasma zone. Emission spectroscopy shows that carbon dioxide forms carbon species during its decomposition in the plasma, we hypothesize that these released carbon species might influence the environment for local nucleation of solid carbon. Thus, the C/O ratio and available carbon fraction for growth cannot always be used to tailor the carbon microstructure. Moreover, the source of oxygen atoms also seems to have an effect on the resultant microstructure.

Recombination of oxygen atoms on the surface of oxidized polycrystalline nickel—temperature and pressure dependences

The recombination of neutral oxygen atoms in the ground state on the oxidized nickel samples was studied experimentally in the range of pressures where the maximum density occurs in weakly ionized low-pressure oxygen plasma, i.e. between 40 and 200 Pa. The recombination coefficient was determined in the flowing afterglow. The source of oxygen atoms was plasma sustained in a quartz tube of inner diameter 4.7 mm by a microwave discharge in the surfatron mode. The recombination coefficient was determined in the afterglow chamber, which was a Pyrex tube with an inner diameter of 36 mm. The density of oxygen atoms in the afterglow chamber was varied by adjusting the discharge power, the gas flow, the pressure, and the position of a recombinator. Such flexibility of the experimental system enabled adjustment of the temperature of the oxidized nickel samples independently from the O-atom density in its vicinity or other parameters. The density of oxygen atoms in the afterglow chamber at various system parameters was determined by the Šorli method, which is reliable, and has an accuracy of about 20%. The recombination coefficient was determined by calorimetry. The coefficient was inversely proportional to the square root of the pressure and exponentially to the sample temperature. Systematic measurements performed at various pressures and temperatures enabled empirical formula, which were explained qualitatively by recombination kinetics.

CO2 as the main parent source of atomic oxygen in comet C/2017 K2 (Pan-STARRS)

C/2017 K2 (Pan-STARRS) is an Oort cloud comet discovered in May 2017. Ground observations have revealed that this long-period comet was active at heliocentric distance of 35 au. At such a distance, activity cannot be driven by the sublimation or the exothermic crystallization of water ice. We assume that the activity of comet C/2017 K2 may be driven by the sublimation of super-volatile ices such as CO and CO2. The nature of parent molecules driving the unprecedented activity of comet C/2017 K2 can be investigated by analyzing its spectrum. In particular, the analysis of atomic oxygen emission lines and the calculation of the green (5577.339 Å) to red (6300.304 and 6363.776 Å) line intensity ratio (hereafter G/R) can reveal the nature of molecules driving cometary activity. We report on the detection of atomic oxygen lines in the spectra of comet C/2017 K2 (Pan-STARRS) from high-resolution spectra obtained at the Telescopio Nazionale Galileo (TNG) on 24 June and 2 July 2022 using the High Accuracy Radial velocity Planet Searcher North (HARPS-N) echelle spectrograph. We found G/R ratios equal to 0.29±0.02 (24 July 2022) and 0.27±0.01 (2 July 2022), which are consistent with a cometary activity driven by CO2, even if located at 2.8 au from the Sun. To better define the nature of the driving molecule, we measured the width of the three oxygen lines and found that the green line in the spectrum of 24 July 2022 is wider than either of the two red lines. This allows us to argue that CO2 is dissociated by highly energetic solar photons that produce O(1S) with a large excess velocity.

Feasibility Study of the Bare-Photovoltaic-Tether Concept: Prototypes and Experimental Performance Evaluation of the Photovoltaic Tether Segment

Consumable-free electron emitters are presently not feasible for autonomous tether-based deorbit devices such as E.T.PACK due to their power requirement. The bare-photovoltaic-tether (BPT) concept combines the bare tether electron collection with a tether segment, coated with thin film Copper Indium Gallium Selenide solar cells to harvest additional power for the cathodic contact, potentially enabling propellant-less operation. This thesis presents the first prototype of the photovoltaic tether segment, its architecture, its electrical characteristics, major challenges of the system and possible solutions. Photovoltaic tether segments of up to 3 m in length were manufactured, consisting of parallelized submodules of 25 cm in length. Due to space limitations, only the I-V-characteristics of these submodules were measured under a self-built Class BCA LED Solar-Simulator inside a vacuum chamber and at varying temperatures between −100 °C and 100 °C. In addition, the suitability of the concept for a low Earth orbit environment was assessed by performing atomic oxygen exposure tests using a microwave-based low pressure plasma atomic oxygen source. Based on the experimental data, a model is provided for predicting the performance of the photovoltaic segment in orbit, highlighting the main problems of the BPT: temperature, orientation and partial shading.

Pathways of N2O production by marine ammonia-oxidizing archaea determined from dual-isotope labeling

The ocean is a net source of the greenhouse gas and ozone-depleting substance, nitrous oxide (N2O), to the atmosphere. Most of that N2O is produced as a trace side product during ammonia oxidation, primarily by ammonia-oxidizing archaea (AOA), which numerically dominate the ammonia-oxidizing community in most marine environments. The pathways to N2O production and their kinetics, however, are not completely understood. Here, we use 15N and 18O isotopes to determine the kinetics of N2O production and trace the source of nitrogen (N) and oxygen (O) atoms in N2O produced by a model marine AOA species, Nitrosopumilus maritimus. We find that during ammonia oxidation, the apparent half saturation constants of nitrite and N2O production are comparable, suggesting that both processes are enzymatically controlled and tightly coupled at low ammonia concentrations. The constituent atoms in N2O are derived from ammonia, nitrite, O2, and H2O via multiple pathways. Ammonia is the primary source of N atoms in N2O, but its contribution varies with ammonia to nitrite ratio. The ratio of 45N2O to 46N2O (i.e., single or double labeled N) varies with substrate ratio, leading to widely varying isotopic signatures in the N2O pool. O2 is the primary source for O atoms. In addition to the previously demonstrated hybrid formation pathway, we found a substantial contribution by hydroxylamine oxidation, while nitrite reduction is an insignificant source of N2O. Our study highlights the power of dual 15N-18O isotope labeling to disentangle N2O production pathways in microbes, with implications for interpretation of pathways and regulation of marine N2O sources.

Anaerobic Hydroxylation of C(sp3)-H Bonds Enabled by the Synergistic Nature of Photoexcited Nitroarenes.

A photoexcited-nitroarene-mediated anaerobic C-H hydroxylation of aliphatic systems is reported. The success of this reaction is due to the bifunctional nature of the photoexcited nitroarene, which serves as the C-H bond activator and the oxygen atom source. Compared to previous methods, this approach is cost- and atom-economical due to the commercial availability of the nitroarene, the sole mediator of the reaction. Because of the anaerobic conditions of the transformation, a noteworthy expansion in substrate scope can be obtained compared to prior reports. Mechanistic studies support that the photoexcited nitroarenes engage in successive hydrogen atom transfer and radical recombination events with hydrocarbons, leading to N-arylhydroxylamine ether intermediates. Spontaneous fragmentation of these intermediates leads to the key oxygen atom transfer products.

Silver-mediated Room Temperature Reactions for the Synthesis of N-α-Ketoacyl Sulfoximines and N-α,β-Unsaturated Acyl Sulfoximines.

Here, we report a silver-mediated coupling of acetylenes with sulfoximines to synthesize N-α-ketoacyl sulfoximines and N-α,β-unsaturated acyl sulfoximines. The reactions are performed under an open atmosphere using the oxidant K2S2O8 and the ligand 2,2-bipyridyl. However, the fate of the product formation is controlled by the type of substrate used. The coupling between aryl acetylenes and sulfoximines afforded the N-α-ketoacylsulfoximines, while the alkyl acetylenes provided the N-α,β-unsaturated acyl sulfoximines. Controlled experiments reveal the differential reactivity patterns of substrates. The labeling 18O experiments showed that water is the source of the incoming oxygen atom for the keto group of N-α-ketoacyl sulfoximines and N-α,β-unsaturated acyl sulfoximines.

Interfacial synergy of Pt cocatalyst and oxygen defective Bi2MoO6 for boosting the photocatalytic redox reaction

Photocatalytic redox reactions using dioxygen as the source of oxygen atoms provide an ideal route for transforming organic compounds into high-value chemicals under mild conditions.

Amine-catalyzed metal-free deamination of propargylamines with water toward chalcones

A non-metal catalyzed deamination of propargylamines was achieved by using DBU as the catalyst and water as the carbonyl oxygen atom source. The role of DBU was found to promote the alkyne-allene isomerization process, followed by the hydrolysis to access a wide range of chalcones in good to excellent yields. This newly developed strategy features metal-free, good functional group compatibility, mild conditions, and operational simplicity.

Easy Access to N-(Pyridin-2-yl)benzamides through Electro-oxidative Ring Opening of 2-Arylimidazo[1,2-a]pyridines

AbstractAn electro-oxidative method for the ring opening of imidazopyridine derivatives is reported. This mild protocol offers a sustainable alternative to the existing harsh reaction conditions and unleashes an efficient approach to produce N-(pyridin-2-yl)amide derivatives with good tolerance of different functional groups. Systematic mechanistic studies provided insight into the reaction pathway and revealed that the residual water of DMSO is the source of oxygen atoms in the products.

Copper/Iodine‐Catalyzed Hydroxyamination of Alkenyl Keto Oximes Using DMSO as the Oxygen Atom Source and Medium

AbstractA new copper/I2‐catalyzed hydroxyamination of alkenes of unsaturated keto oximes with DMSO as the hydroxy oxygen atom source and medium for assembling 2‐(2‐hydroxyalkyl)‐3,4‐dihydro‐2H‐pyrrole 1‐oxides is described. Mechanistic studies suggest that the reaction is terminated by a single electron oxidation and subsequent nucleophilic reaction.

Oxygen atom density in a large reactor powered by four inductively coupled plasma sources

Gradients in O-atom density in metallic plasma reactor useful for rapid surface activation of 3D polymer products have been measured. The reactor of a volume of 150 l was equipped with four inductively coupled plasma sources (ICPS) of (predominantly) oxygen atoms, parallelly coupled with a radio-frequency generator of adjustable power up to 5 kW at 13.56 MHz. Molecular oxygen was continuously introduced into the ICP sources, where it was dissociated upon plasma conditions. The constant pumping of the plasma reactor enabled the effective transfer of O-atoms from the ICP sources, so that their density remained high in the entire chamber even far from plasma sources. The O-atom density was measured across the reactor with a movable catalytic probe calibrated for oxygen. The sophisticated immersible design enabled the O-atom density to exceed 1021 m−3 in the major chamber volume at the pressure of 20 Pa. At this pressure, a uniform plasma in the H-mode was sustained at the total real RF power of 1800 W. Significant gradients in the O-atom density were only detected next to ICP sources' exhausts and in the main chamber's metallic side tubes. Such uniform distribution of O-atoms in a large reactor is advantageous for rapid surface activation of 3D polymer products.

Molecular beam epitaxy of Sr5Au2O8 thin films

The synthesis of complex transition metal oxides using molecular beam epitaxy is well established with the exception of gold. Overcoming the oxophobicity of gold is a mandatory step towards an entire new section of complex transition metal oxides. Here, we show that ${\mathrm{Sr}}_{5}{\mathrm{Au}}_{2}{\mathrm{O}}_{8}$ thin films can be epitaxially grown onto ${\mathrm{SrTiO}}_{3}$ substrates using a high-efficiency radio-frequency-operated atomic oxygen source as an oxidizing agent. Stoichiometric atomic beam fluxes of strontium and gold were controlled by electron-impact emission spectroscopy. ${\mathrm{Sr}}_{5}{\mathrm{Au}}_{2}{\mathrm{O}}_{8}$ thin films were grown at temperatures between 627 and 653 ${}^{\ensuremath{\circ}}\mathrm{C}$. Owing to the sensitivity of ${\mathrm{Sr}}_{5}{\mathrm{Au}}_{2}{\mathrm{O}}_{8}$ thin films to environmental agents, e.g., water and ${\mathrm{CO}}_{2}$, we capped them with a 300-nm layer of Se or a 200-nm layer of Au.

Electrochemical Scalable Sulfoxidation of Sulfides with Molecular Oxygen and Water

AbstractAn efficient and chemoselective synthesis of sulfoxides through the electrooxidation of sulfides has been well developed. This protocol takes advantage of electricity as the terminal oxidant and of molecular oxygen and water as the oxygen atom sources. A variety of structurally diverse sulfoxide compounds are assembled in moderate to excellent yields. The scaled‐up reactions at 6–20 mmol show the good practicability and application potential of this methodology. A possible free radical mechanism has been proposed to rationalize the reaction procedure.